U.S. patent application number 10/137248 was filed with the patent office on 2003-10-30 for method and apparatus for selecting an optimal electrode configuration of a medical electrical lead having a multiple electrode array.
Invention is credited to Cho, Yong Kyun, McClure, Lawrence C., Sommer, John L..
Application Number | 20030204232 10/137248 |
Document ID | / |
Family ID | 29249731 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030204232 |
Kind Code |
A1 |
Sommer, John L. ; et
al. |
October 30, 2003 |
Method and apparatus for selecting an optimal electrode
configuration of a medical electrical lead having a multiple
electrode array
Abstract
An electrical medical lead is provided having two or more
electrodes, electrically insulated from each other and electrically
coupled to individually insulated filars in a multi-filar coiled
conductor. When the lead is used with a medical device equipped
with a switch matrix, electrodes are selected individually or
simultaneously to serve as an anode or cathode in any unipolar,
bipolar or multi-polar configuration for delivering stimulation
and/or sensing signals in excitable tissue. In one embodiment, a
tip electrode array is expandable for improving electrode contact
with targeted tissue and stabilizing lead position.
Inventors: |
Sommer, John L.; (Coon
Rapids, MN) ; Cho, Yong Kyun; ( Maple Grove, MN)
; McClure, Lawrence C.; (Forest Lake, MN) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARKWAY NE
MS-LC340
MINNEAPOLIS
MN
55432-5604
US
|
Family ID: |
29249731 |
Appl. No.: |
10/137248 |
Filed: |
April 30, 2002 |
Current U.S.
Class: |
607/122 |
Current CPC
Class: |
A61B 5/282 20210101;
A61N 1/3704 20130101; A61N 1/3686 20130101; A61N 1/056 20130101;
A61N 1/36185 20130101; A61B 5/7217 20130101; A61N 1/0573 20130101;
A61N 1/05 20130101 |
Class at
Publication: |
607/122 |
International
Class: |
A61N 001/05 |
Claims
We claim:
1. An implantable electrical lead, comprising: an elongated lead
body extending between a proximal lead end and distal lead end; a
plurality of electrodes located along the distal lead end; an
insulating material positioned between each of the plurality of
electrodes to electrically isolate each of the plurality of
electrodes; a plurality of insulated electrical conductors each
connected to a respective electrode of the plurality of electrodes;
and a microprocessor performing a threshold search corresponding to
combinations of one or more electrodes of the plurality of
electrodes to determine an optimal threshold, and selecting the
electrodes of the plurality of electrodes corresponding to the
optimal threshold.
2. The implantable medical lead of claim 1, wherein the threshold
search corresponds to a pacing threshold measurement.
3. The implantable medical lead of claim 1, wherein the selected
electrodes are used for delivering electrical impulses.
4. The implantable medical lead of claim 1, wherein the threshold
search corresponds to a sensing threshold measurement.
5. The implantable medical lead of claim 4, wherein the sensing
threshold measurement further includes determining a
signal-to-noise ratio.
6. The implantable medical lead of to claim 4, wherein the
functioning electrode configuration is used for sensing
depolarization signals.
7. The implantable medical lead of claim 1, wherein the plurality
of electrodes are circumferentially arranged along the lead.
8. The implantable medical lead of claim 7, wherein the plurality
of electrodes are arranged in a staggered relative position.
9. The implantable medical lead of claim 1, wherein the plurality
of electrodes are positioned in a longitudinally-spaced ring
arrangement.
10. The implantable medical lead of claim 1, wherein selecting the
electrodes of the plurality of electrodes corresponding to the
optimal threshold is performed manually.
11. The implantable medical lead of claim 1, wherein selecting the
electrodes of the plurality of electrodes corresponding to the
optimal threshold is performed automatically.
12. The implantable medical lead of claim 1, further comprising an
expansion member expanding the plurality of electrodes to vary an
inter-electrode distance, wherein the threshold search is performed
corresponding to the varied inter-electrode distance.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an implantable
electrical stimulation and/or sensing lead, and more particularly,
the present invention relates to a method and apparatus for
improved stimulation and sensing of a medical electrical lead
having a multiple electrode array.
BACKGROUND OF THE INVENTION
[0002] A wide assortment of implantable medical devices (IMDs) are
presently known and in commercial use. Such devices include cardiac
pacemakers, cardiac defibrillators, cardioverters,
neurostimulators, and other devices for delivering electrical
signals to excitable tissue and/or receiving signals from the
tissue. Devices such as pacemakers, whether implantable or
temporary external type devices, are part of a system for
delivering an electrical therapy or monitoring a patient condition.
In addition to the pacemaker device, which typically has some form
of pulse generator, a pacing system includes one or more leads
carrying electrodes for delivering generated stimulation pulses to
the heart and for sensing cardiac signals.
[0003] Pacemakers treat heart conditions in which the heart beats
at a rate that is considered to be too slow, commonly referred to
as bradycardia, by sensing cardiac signals and delivering
appropriately timed electrical stimulation pulses to the atria
and/or ventricles as needed to cause the myocardium to contract.
Pacemakers may sense intrinsic cardiac signals that occur when the
myocardium depolarizes naturally, causing a normal myocardial
contraction or heart beat. A sensed signal associated with
ventricular contraction is referred to as an R-wave, and a sensed
signal associated with atrial contraction is a P-wave. When an
intrinsic R-wave or P-wave is not sensed by the pacemaker, a
stimulation pacing pulse is delivered, eliciting an evoked response
which causes the myocardium to contract, thus maintaining a desired
heart rate.
[0004] Pacemakers operate in either a unipolar or bipolar mode, and
pace the atria and/or the ventricles of the heart. Unipolar pacing
requires a lead having only one distal electrode for positioning in
the heart, and utilizes the case, or housing of the implanted
device as the other electrode for the pacing and sensing
operations. For bipolar pacing and sensing, the lead typically has
two electrodes, a tip electrode disposed at the distal end of the
lead, and a ring electrode spaced somewhat back from the distal
end. Each electrode is electrically coupled to a conductive cable
or coil, which carries the stimulating current or sensed cardiac
signals between the electrodes and the implanted device via a
connector.
[0005] Combination devices are available for treating both fast and
slow cardiac arrhythmias by delivering electrical shock therapy for
cardioverting or defibrillating the heart in addition to cardiac
pacing therapies. Such a device, commonly known as an implantable
cardioverter defibrillator or "ICD", uses coil electrodes for
delivering high-voltage shock therapies. An implantable cardiac
lead used in combination with an ICD may be a tripolar or
quadrapolar lead equipped with a tip electrode and a ring electrode
for pacing and sensing functions and one or two coil electrodes for
shock therapies.
[0006] In order to achieve stimulation or sensing in the right side
of the heart, a lead may be positioned against the endocardium by
advancing the lead through the vena cava into the right atrium for
right atrial applications, or further advancing the lead into the
right ventricle for right ventricular applications. In order to
achieve stimulation or sensing in the left heart chambers, a lead,
often referred to as a "coronary sinus lead," may be positioned
within the vasculature of the left side of the heart via the
coronary sinus and great cardiac vein. This endovascular lead
placement is sometimes referred to as "epicardial" placement since
electrodes on a coronary sinus lead will sense or stimulate
epicardial heart tissue.
[0007] In order to work reliably, cardiac leads need to be
positioned and secured at a targeted cardiac tissue site in a
stable manner. Unacceptable pacing or sensing thresholds measured
during an implant procedure may require lead repositioning.
Shifting or dislodgement of the lead over time may result in
changing thresholds, sometimes requiring programming adjustments in
order to maintain an appropriate level of therapy. At the same
time, increased pacing thresholds decrease the useful life of the
battery in the implantable device, requiring earlier device
replacement. Poor or inaccurate sensing of naturally occurring
heart signals may result in inappropriate withholding or delivery
of therapy.
[0008] To address these problems, an electrode may be passively
secured in a desired endocardial position by the use of tines
located at the distal end of a lead. The tines engage with the
endocardial trabeculae, holding the distal lead end in place.
Alternatively, an electrode may be actively secured by the use of a
rotatable fixation helix. The helix exits the distal end of the
lead and can be screwed into the body tissue. The helix itself may
serve as an electrode or it may serve exclusively as an anchoring
mechanism to locate an electrode mounted on the lead adjacent to a
targeted tissue site. The fixation helix may be coupled to a drive
shaft that is further connected to a coiled conductor that extends
through the lead body as generally described in U.S. Pat. No.
4,106,512 issued to Bisping et al. A physician rotates the coiled
conductor at a proximal end to cause rotation of the fixation helix
via the drive shaft. As the helix is rotated in one direction, the
helix is secured in the cardiac tissue. Rotation of the fixation
helix in the opposite direction removes the helix from the tissue
to allow for repositioning of the lead at another location.
[0009] These fixation methods, however, are not entirely
appropriate in left heart stimulation and sensing applications when
the lead is positioned endovascularly. A helical coil would
puncture a cardiac vein. Tines would make lead re-positioning
difficult because retraction of a tined lead within a narrow vein
could potentially damage the valves within the vein. Tissue
encapsulation of various passive and active fixation devices is
normally encouraged to further stabilize an endocardial lead
position. Tissue encapsulation is undesirable in stabilizing an
endovascular lead, however, since such tissue ingrowth may obstruct
blood flow. Methods for stabilizing an endovascular lead must allow
for unimpeded blood flow. One method for stabilizing an
endovascular lead is disclosed in U.S. Pat. No. 6,161,029, issued
to Spreigl, et al., and includes an expanded stent that is lodged
against the blood vessel wall to inhibit movement of the stent and
a distal electrode support. The expanded stent lumen is aligned
with the electrode support lumen for allowing blood to flow through
the aligned electrode support lumen and expanded stent lumen.
[0010] Another problem encountered in left heart stimulation is
that conventional circumferential tip or ring electrodes on a
coronary sinus lead will direct current in the direction of the
adjacent epicardium but also in directions away from the targeted
tissue, which may reduce stimulation efficiency. Stray current may
also cause undesired extraneous stimulation, such as phrenic nerve
stimulation or atrial stimulation during ventricular pacing. A
coronary sinus lead would preferably direct current only in the
direction of the targeted myocardium. Correctly positioning an
endovascular lead having an electrode on only one side, however,
would be difficult and time consuming.
[0011] Lead failure sometimes occurs when a conductor becomes
fractured or the insulation between electrodes and/or conductors
fails. A unipolar lead failure generally requires a surgical
procedure to replace the failed lead. In the case of a bipolar
lead, a bipolar stimulation or sensing configuration may be
reprogrammed to unipolar if one electrode on the lead remains
functional. However, the remaining functional electrode may be
positioned at a different location relative to the targeted cardiac
tissue and may not provide as effective or efficient sensing or
stimulation as the bipolar pair. Furthermore, in some patients,
unipolar sensing does not provide an acceptable signal-to-noise
ratio.
[0012] For effective cardiac pacing, a delivered stimulation pulse
must be of adequate energy to cause depolarization of the
myocardium, referred to as "capture." The lowest pulse energy that
successfully captures the heart is referred to as the pacing
threshold. In order to verify that a pacing pulse has captured the
heart, modern pacemakers are equipped with automatic capture
detection algorithms. Capture may be verified by various
methodologies known in the art such as sensing for an evoked R-wave
or P-wave after delivery of a pacing pulse, sensing for the absence
of an intrinsic R-wave or P-wave during the refractory period after
a pacing pulse, or detecting a conducted depolarization in an
adjacent heart chamber. Various capture verification methods are
described in U.S. Pat. No. 5,601,615 issued to Markowitz et al.,
U.S. Pat. No. 5,324,310 issued to Greeninger et al., and U.S. Pat.
No. 5,861,012 issued to Stroebel, each of which patents are
incorporated herein by reference in their entirety. If capture is
not verified, the pacing pulse energy may be automatically
increased.
[0013] An electrode configuration used for pacing and evoked
response sensing for capture detection may utilize a bipolar lead
on which a tip electrode provides unipolar pacing and the tip and
ring electrode pair provide bipolar sensing of the evoked response.
A limitation of using the same electrode for pacing and evoked
response sensing is that the pacing pulse and ensuing
after-potential and electrode-tissue polarization artifact mask the
evoked response until they dissipate, after which the evoked
response, if any, has typically passed the sensing electrodes.
Therefore, it is desirable to use an electrode pair that does not
include the pacing electrode for sensing an evoked response. To
overcome the problems of after-potential and the electrode-tissue
polarization artifact, capture verification methods have been
proposed which involves sensing for a conducted depolarization at a
site away from the pacing electrode. For example, sensing a
ventricular depolarization after an atrial pacing pulse has been
delivered is evidence that the atrium was captured and the evoked
depolarization was conducted to the ventricle.
[0014] For accurate evoked response detection, however, it is
desirable to sense the evoked response using a bipolar sensing
electrode pair in the vicinity of the stimulated cardiac tissue
site. Unipolar sensing or sensing in other areas of the heart could
lead to erroneous evoked response detection due to noise or other
myopotentials being sensed as an evoked response. Furthermore,
sensing for an evoked response in another area of the heart may not
be possible in patients having conduction disorders.
[0015] What is needed, therefore, is an improved lead design that
allows accurate targeting of excitable tissue in both endovascular
and endocardial applications. A lead having an electrode
arrangement that allows for reliable pacing and evoked response
sensing for the purpose of capture verification is also desirable.
Such a lead must be stabilized in a way that, when used
endovascularly, does not cause undue vessel damage during fixation
or repositioning and allows for unimpeded blood flow. Furthermore,
an improved lead design should provide for alternative stimulation
or sensing configurations without compromising effectiveness and
efficiency of therapy delivery in case one electrode fails.
SUMMARY OF THE INVENTION
[0016] The present invention is directed to implantable electrical
lead that includes an elongated lead body that extends between a
proximal lead end and distal lead end, and a plurality of
electrodes located along the distal lead end. An insulating
material is positioned between each of the plurality of electrodes
to electrically isolate each of the plurality of electrodes, and a
plurality of insulated electrical conductors are each connected to
a respective electrode of the plurality of electrodes. A
microprocessor performs a threshold search corresponding to
combinations of one or more electrodes of the plurality of
electrodes to determine an optimal threshold, and selects the
electrodes of the plurality of electrodes corresponding to the
optimal threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Features and advantages of the present invention will be
readily appreciated as the invention becomes better understood by
reference to the following detailed description considered in
connection with the accompanying drawings, in which like reference
numerals designate like parts throughout:
[0018] FIG. 1 is a plan view of an implantable electrical lead
having a tip electrode array and a ring electrode array;
[0019] FIG. 2 is a perspective view of a distal end of the lead
shown in FIG. 1;
[0020] FIG. 3 is a plan view illustrating alternative arrangements
of electrodes within an electrode array according to the present
invention;
[0021] FIG. 4 is a side, cut-away view of the distal lead end shown
in FIG. 2;
[0022] FIG. 5 is a side, cut-away view of a distal lead end of an
implantable electrical lead having a helical expansion member for
expanding a tip electrode array;
[0023] FIG. 6 is a side cut-away view of the distal lead end shown
in FIG. 5 showing a tip electrode array in a fully expanded
position;
[0024] FIG. 7 is a side, cut-away view of a distal lead end having
an alternative expansion member for expanding a tip electrode array
according to the present invention;
[0025] FIG. 8 is an illustration showing the lead of FIG. 1
implanted within the coronary vessels of a patient's heart via the
coronary sinus and in communication with an implantable
cardioverter defibrillator, according to a preferred embodiment of
the present invention;
[0026] FIG. 9 is a functional, block diagram of the implantable
cardioverter defibrillator (ICD) shown in FIG. 8; and
[0027] FIG. 10 is a flow chart of a method for using the lead shown
in FIG. 8 in conjunction with the implantable cardioverter
defibrillator (ICD) of FIG. 9.
DETAILED DESCRIPTION OF THE INVENTION
[0028] In the following detailed description, references are made
to illustrative embodiments of medical leads adapted to be located
in the heart or cardiac blood vessels in which aspects of the
present invention may be implemented. It is understood that the
invention may be practiced in other body implantable leads
positioned for sensing or stimulating excitable tissue.
[0029] FIG. 1 is a plan view of a multipolar cardiac lead in
accordance with an embodiment of the present invention. As
illustrated in FIG. 1, a lead 10 according to the present invention
includes an elongated lead body 12 having a connector assembly 16
at a proximal end adapted for connecting to an implantable device,
such as an ICD, and an electrode head assembly 68 at a distal end
14 for carrying one or more electrodes. Lead 10 is shown having, at
or near distal end 14, a tip electrode array 20, a ring electrode
array 30, a ring electrode 40, and a defibrillation coil electrode
50. The tip electrode array 20 and the ring electrode array 30 each
include multiple electrodes, for example three electrodes,
separated by insulating material. Electrodes within the tip
electrode array 20 and/or ring electrode array 30 and/or ring
electrode 40 may be utilized to sense cardiac signals and/or
deliver pacing pulses to a patient's heart. The defibrillation coil
electrode 50 is used for delivery of a defibrillation shock as a
result of a detected tachycardia or fibrillation condition.
[0030] The lead body 12 takes the form of an extruded tube of
biocompatible plastic such as silicone rubber. The lead body 12
includes multiple lumens for carrying multiple insulated conductors
from the connector assembly 16 to the corresponding electrodes
arrays 20 and 30 and electrodes 40 and 50 located at or near the
distal lead end 14. The multi-lumen lead body 12 may correspond
generally to that disclosed in U.S. Pat. No. 5,584,873 issued to
Shoberg et al., incorporated herein by reference in its entirety.
Two of the insulated conductors carried by lead body 12 may be
stranded or cabled conductors, each electrically coupled to one of
the ring electrode 40 and the defibrillation coil 50. The cabled
conductors may correspond generally to the conductors disclosed in
U.S. Pat. No. 5,246,014, issued to Williams et al., incorporated
herein by reference in its entirety. A third and fourth conductor
are preferably multi-filar coiled conductors, for example of the
type described in U.S. Pat. No. 4,922,607 issued to Doan et al.,
incorporated herein by reference in its entirety. Each filar of the
multi-filar coiled conductors is coupled to an individual electrode
within the tip electrode array 20 or the ring electrode array 30.
The filars are electrically insulated from each other for example
by polytetrafluoroethylene (PTFE) or ethyl tetrafluoroethylene
(ETFE) tubing.
[0031] The connector assembly 16 includes multiple connector
extensions 22, 32, and 52 arising from a trifurcated connector
sleeve 18, typically formed of silicone rubber. The connector
extensions 22, 32 and 52 couple the lead 10 to an implantable
medical device such as an implantable cardioverter defibrillator
(ICD).
[0032] Connector extension 22 is shown as a tri-polar connector
including three connector rings 24. Connector extension 22 houses a
multi-filar coiled conductor of which each filar is electrically
coupled at a proximal end to one of the connector rings 24 and at a
distal end to one of the three electrodes included in tip electrode
array 30. A stylet 60 may be advanced within an inner lumen of the
coiled conductor carried by connector extension 22 toward the
distal end of the lead 10 to aid in lead placement during an
implant procedure.
[0033] Connector extension 32 is shown as a quadrapolar connector
including three connector rings 34 and a fourth connector ring 36.
The three connector rings 34 are electrically coupled to individual
filars within a multi-filar coiled conductor extending to the ring
electrode array 30. The distal end of each filar is coupled to one
of three electrodes included in ring array 30. The fourth connector
ring 36 is coupled to an insulated cabled conductor that extends to
ring electrode 40.
[0034] Connector extension 52 carries a single connector pin 54
that is electrically coupled to an insulated cable extending the
length of the lead body 12 and electrically coupled to the
defibrillation coil electrode 50. While the lead 10 depicted in
FIG. 1 is a multi-polar pacing and defibrillation lead, aspects
included in the invention may be practiced in any unipolar,
bipolar, or multi-polar lead by providing at least one tip or ring
electrode array. One or more electrode arrays may be provided alone
or with any combination of conventional tip, ring or coil
electrodes.
[0035] FIG. 2 is an enlarged, perspective view of the electrode
head assembly 68 located at the distal lead end 14 shown in FIG. 1.
The tubular electrode head assembly 68 is preferably fabricated
from a relatively rigid biocompatible polymer, such as
polyurethane. As illustrated in FIG. 2, tip electrode array 20,
mounted on the tip of the electrode head assembly 68, includes
three approximately equally sized electrodes 25, 27 and 29 arranged
circumferentially with respect to the electrode assembly 68. The
tip electrode array 20 could alternatively comprise two or more
electrodes of approximately equal or unequal sizes. The electrodes
25, 27 and 29 are preferably platinum iridium electrodes, but may
be manufactured from any acceptable, medical grade, conductive
biomaterial. A layer of insulating material 64, such as ceramic, is
arranged radially with respect to the electrode head assembly 68,
between each of the electrodes 25, 27 and 29 such that the
electrodes 25, 27 and 29 within the array 20 are electrically
insulated from each other.
[0036] The insulator 64 optionally provides a center port 56. When
the electrode array 20 is used as a tip electrode, as shown in FIG.
1, the port 56 may be used to hold a pharmaceutical agent. The
pharmaceutical agent, which may be an anti-inflammatory,
antibiotic, or other agent, may be added as a powdered form to a
polymer adhesive that is injected into port 56 such that the agent
elutes from the polymer over time after implantation. In one
embodiment, the port 56 holds a steroid powder added to medical
grade silicone adhesive, which when released after implantation
will minimize the inflammatory tissue response around the electrode
array 20. Various embodiments for providing a drug dispenser in an
electrical medical lead that may be used in conjunction with the
present invention are disclosed in U.S. Pat. No. 4,711,251 issued
to Stokes, incorporated herein by reference in its entirety.
[0037] In the same way, the ring electrode array 30 includes three,
approximately equally-sized, circumferentially arranged electrodes
separated from each other by a layer of insulating material 66.
FIG. 3 illustrates alternative arrangements of electrodes within an
electrode array. In the alternative tip electrode 120, three
electrodes 125, 127, and 129 are arranged circumferentially around
the electrode head assembly 68 but staggered along its length such
that electrode 125 is located at the distal lead tip, electrode 129
is located slightly proximal to electrode 125, and electrode 127 is
slightly proximal to electrode 129. This staggered arrangement
could equally be applied to a ring electrode array.
[0038] The ring electrode array 130 shown in FIG. 3 includes three
ring electrodes 135, 137, and 139, each encircling electrode head
assembly 68 and spaced at close intervals longitudinally with
respect to each other along the electrode head assembly 68. This
longitudinally-spaced ring arrangement could also be applied to a
tip electrode array. It is recognized that numerous variations of
electrode array arrangements may exist in which two or more
electrodes are arranged in close proximity to each other.
[0039] FIG. 4 is a side cut-away view of the tubular electrode head
assembly 68 of the lead 10 shown in FIG. 2. Electrodes 27 and 29
included in tip array 20 are visible in this view, and electrodes
37 and 39 of ring array 30 are visible in this view. Electrodes 27
and 29 included in tip array 20 are each provided with connection
tabs 82 to allow electrical coupling, for example by laser welding,
to individual filars 84 included in the multi-filar coiled
conductor 80. Multi-filar conductor 80 is connected at a proximal
end to connector rings 24 (FIG. 1). Insulation material 64 is shown
between electrodes 27 and 29.
[0040] Electrodes 37 and 39 included in ring array 30 are each
provided with connection tabs 92 to allow electrical coupling to
individual filars 94 included in the multi-filar coiled conductor
90. Multi-filar conductor 90 is connected at its proximal end to
connector rings 34 (FIG. 1). Ring electrode 40 is shown coupled to
cabled conductor 70, which is further coupled at its proximal end
to connector ring 36. By providing separate, insulated conductors
to each of the insulated electrodes 25, 27, 29 of tip array 20 and
35, 37 and 39 of ring array 30, the electrodes 25, 27, 29, 35, 37
and 39 may be selected individually or in any combination for
pacing and/or sensing functions.
[0041] An alternative embodiment of the lead 10 is shown by the
side cutaway view of FIG. 5. In this embodiment, the tip electrode
array 20 is expandable. The electrodes 27 and 29 within array 20
are mounted on flexible electrode extensions 87 and 89,
respectively. An expansion member for expanding the flexible
electrode extensions 87 and 89 takes the form of a conically-shaped
helix 100. The helix 100 may function exclusively as an expansion
member, in which case the helix may be formed from any relatively
rigid biocompatible polymer, such as urethane, or a biocompatible
metal. The tip of helix 100 may be blunted to prevent unintentional
tissue damage. In other embodiments, the helix 100 may also serve
as an additional electrode for cardiac pacing and/or sensing. When
used as an electrode, the helix 100 is formed from a conductive
biocompatible metal such as platinum iridium alloy. The helix 100
may also serve as an active fixation device for anchoring the lead
10 in a desired position for additional stability. In this case,
the helix 100 has a sharpened tip for securing the helix 100 in
tissue. Reference is made to U.S. Pat. No. 4,217,913 issued to
Dutcher, incorporated herein by reference in its entirety.
[0042] The helix 100 is shown in FIG. 5 to be mounted on a drive
shaft 102 that is further connected to a rotatable coil 110. The
coil 110 extends the length of the lead body 12 and may be coupled
to a connector pin provided on one of the connector extensions of
connector assembly 16. During a lead implant or explant procedure,
a physician may rotate such a connector pin relative to the
connector assembly 16 causing advancement or retraction of the
helix 100 in a manner generally described in U.S. Pat. No.
4,106,512 to Bisping et al., incorporated herein by reference in
its entirety. Rotation of the connector pin rotates the drive shaft
102 via the coil 110. As the drive shaft 102 is rotated, the helix
100 is actuated by a guide 106 such that the helix 100 is advanced
toward the lead end. A drive shaft seal 104 is optionally provided
to prevent the ingress of body fluids into the lumen of lead
10.
[0043] In FIG. 6, the tip electrode array 20 is shown in a fully
expanded position. The helix 100 is in an advanced position such
that the widest portion of the conical helix 100 has caused the
flexible electrode extensions 87 and 89, each carrying one of the
electrodes 27 and 29 included in tip array 20, to bend outward.
[0044] Expansion of the tip array 20 in this way provides a passive
fixation mechanism for stabilizing the lead position. When used as
an endocardial electrode, the expanded electrode array 20 may
engage with the endocardial trabeculae, holding the distal lead end
in place. If the initial lead position does not result in
acceptable pacing or sensing thresholds, the helix 100 may be
retracted, contracting the tip array 20, to allow easy removal and
lead repositioning. This reversible fixation mechanism is
particularly useful when the lead 10 is used as an endovascular
lead. Contraction of the tip array 20 allows easy retraction of the
lead within a narrow vein without undue damage to vessel walls or
vein valves. Furthermore, the expanded electrode array provides
stable lead positioning within a blood vessel without blocking the
flow of blood or puncturing the blood vessel walls.
[0045] Another advantage of expanding the tip electrode array 20
relates to the benefit of increasing the inter-electrode distance
when the tip array 20 is used for pacing and evoked response
sensing. If, for example, one electrode of tip array 20 is used for
pacing in a unipolar configuration with a device housing or in a
bipolar configuration with any of ring electrode array 30 or ring
electrode 40, the remaining two electrodes within tip array 20 are
available for sensing an evoked response in the same vicinity of
the delivered pacing pulse. Sensing for an evoked response at the
site of stimulation delivery enables accurate capture detection
since other myopotentials, which may be present at more remote
sensing sites, are less likely to interfere with evoked response
sensing. By using electrodes different than the electrode used for
pacing, problems associated with post-pace polarization artifacts
can be avoided. The increased inter-electrode distance in an
expanded tip array further enhances the ability to sense the evoked
response using electrodes within the same array because the
post-pace polarization artifact will diminish as the distance from
the placing electrode increases.
[0046] An alternative embodiment of an expansion member is shown in
FIG. 7. In this embodiment, the expansion member takes the form of
a grooved cone 150, which is preferably fabricated from a
biocompatible, relatively rigid polymer such as polyurethane. The
cone 150 is mounted on a drive shaft 152 having a screw-like head
154 with a slot 156. A stylet 158 having a screw driver-like blade
160 mounted on its distal end may be advanced within a lumen of the
lead body 12. The blade 160 may be inserted into slot 156 and, upon
rotation of the stylet 158 at its proximal end, cause rotation of
the drive shaft 152. When the drive shaft 152 is rotated, the cone
150 is actuated by the guide 106 and is advanced toward the distal
lead tip to cause expansion of the tip electrode array 20 mounted
on flexible electrode extensions 87 and 89.
[0047] In one embodiment, the expansion member may be coated with a
substrate or solvent carrying a pharmaceutical agent, such as an
anti-inflammatory drug. The expansion member may be dip-coated in a
solvent, such as acetone, in which a steroid has been dissolved.
The steroid will elute from the coating over time after
implantation and prevent a hyper-inflammatory response at the
implant site. A method for treating an electrode with a steroid
solution, which may be adapted for use in the present invention for
treating the expansion member, is generally described in U.S. Pat.
No. 5,987,746 issued to Williams, incorporated herein by reference
in its entirety.
[0048] In FIG. 8, the lead 10 is shown as a part of a cardiac
stimulation system including an ICD 410 coupled to a patient's
heart 450 by way of lead 10. The ICD 410 is encased in a housing
411 and provided with a connector block 412 to accommodate
connection of lead 10 to the ICD 410. The heart 450 is shown with a
partially open view revealing the coronary sinus 430. The lead 10
is advanced within the vasculature of the left side of the heart
via the coronary sinus and great cardiac vein. A tip electrode
array 20 is disposed in a vascular lumen 440 adjacent the left
ventricle 460. The tip electrode array is shown in an expanded
position at a desired cardiac implantation site. A blunted
expansion cone 150 has been advanced in order to expand the
electrodes within array 20 against the walls of lumen 440 so as to
provide better electrode contact with the epicardial tissue and to
stabilize the position of the lead 10 as previously described in
conjunction with FIG. 7. The coronary sinus lead 10 is also
equipped with a ring electrode array 30, a ring electrode 40 and a
defibrillation coil electrode 50. The coronary sinus lead 10 is
shown connected to the ICD 410 via the trifurcated connector
assembly 16, which accommodates connection of ICD circuitry to the
conductors within lead body 12 and their respective electrodes.
[0049] A functional schematic diagram of the ICD 410 is shown in
FIG. 9. This diagram should be taken as exemplary of one type of
device within a body implantable system that includes a lead having
one or more electrode arrays in accordance with the present
invention. The disclosed embodiment shown in FIG. 9 is a
microprocessor-controlled device, but the methods of the present
invention may also be practiced in other types of devices such as
those employing dedicated digital circuitry.
[0050] With regard to the electrode system illustrated in FIG. 8,
the ICD 410 is provided with a number of connection terminals for
achieving electrical connection to the lead 10 via the connector
assembly 16 and the respective electrodes via their associated
conductors. The connection terminal 311 provides electrical
connection to the housing 411 for use as the indifferent electrode
during unipolar stimulation or sensing. The connection terminal 350
provides electrical connection to the defibrillation coil electrode
50. The connection terminals 311 and 350 are coupled to the high
voltage output circuit 234 to facilitate the delivery of high
energy shocking pulses to the heart using the defibrillation coil
electrode 50 and housing 411.
[0051] The connection terminals 325, 327 and 329 provide electrical
connection to the electrodes 25, 27 and 29, respectively, within
tip electrode array 20. The connection terminals 335, 337 and 339
provide electrical connection to the electrodes 35, 37 and 39,
respectively, within ring electrode array 30. The connection
terminal 340 provides electrical connection to the ring electrode
40. The connection terminals 325, 327, 329, 335, 337, 339, and 340
are further coupled to a switch matrix 208.
[0052] Switch matrix 208 is used to select which of the available
electrodes are coupled to a ventricular sense amplifier (AMP) 200
for sensing ventricular signals. Selection of the electrodes is
controlled by the microprocessor 224 via data/address bus 218. The
selected electrode configuration may be varied according to the
various sensing, pacing, cardioversion and defibrillation functions
of the ICD 410.
[0053] The ventricular sense amplifier 200 preferably takes the
form of an automatic gain controlled amplifier with adjustable
sensing thresholds. The general operation of the ventricular sense
amplifier 200 may correspond to that disclosed in U.S. Pat. No.
5,117,824 issued to Keimel et al., incorporated herein by reference
in its entirety. Whenever a signal received by the ventricular
sense amplifier 200 exceeds a ventricular sensing threshold, a
signal is generated on the R-out signal line 202.
[0054] Switch matrix 208 is also used to select which of the
available electrodes are coupled to a wide band amplifier 210 for
use in digital signal analysis. Signals from the electrodes
selected for coupling to bandpass amplifier 210 are provided to
multiplexer 220, and thereafter converted to multi-bit digital
signals by A/D converter 222, for storage in random access memory
226 under control of direct memory access circuit 228.
Microprocessor 224 may employ digital signal analysis techniques to
characterize the digitized signals stored in random access memory
226 to recognize and classify the patient's heart rhythm employing
any of the numerous signal processing methodologies known in the
art.
[0055] The telemetry circuit 330 receives downlink telemetry from
and sends uplink telemetry to an external programmer, as is
conventional in implantable anti-arrhythmia devices, by means of an
antenna 332. Data to be uplinked to the programmer and control
signals for the telemetry circuit are provided by microprocessor
224 via address/data bus 218. Received telemetry is provided to
microprocessor 224 via multiplexer 220. Numerous types of telemetry
systems known for use in implantable devices may be used.
[0056] The remainder of the circuitry illustrated in FIG. 9 is an
exemplary embodiment of circuitry dedicated to providing cardiac
pacing, cardioversion and defibrillation therapies. The pacer
timing and control circuitry 212 includes programmable digital
counters, which control the basic time intervals associated with
various pacing modes or anti-tachycardia pacing therapies delivered
in the ventricle. Pacer circuitry 212 also determines the amplitude
of the cardiac pacing pulses under the control of microprocessor
224.
[0057] During pacing, escape interval counters within pacer timing
and control circuitry 212 are reset upon sensing of R-waves as
indicated by signals on Rout signal line 202. The durations of the
escape intervals are determined by microprocessor 224 via
data/address bus 218. The value of the count present in the escape
interval counters when reset by sensed R-waves can be used to
measure R-R intervals for detecting the occurrence of a variety of
arrhythmias. In accordance with the selected mode of pacing, if the
ventricular escape interval expires pacing pulses are generated by
ventricular pacer output circuit 216. The pacer output circuit 216
is coupled to the desired pacing electrodes via switch matrix 208
along signal line 217. The escape interval counters are reset upon
generation of pacing pulses, and thereby control the basic timing
of cardiac pacing functions, including antitachycardia pacing. When
a pacing pulse is delivered, a signal is generated by pacer timing
and control 212 on blanking signal line (V BLANK) 211 to prevent
saturation of the sense amplifier 200 during the pacing pulse.
[0058] Thus, complete programmability of the electrodes used in
pacing and/or sensing is possible via switch matrix 208. Any of the
electrodes included in tip array 20, ring electrode array 30 and
ring electrode 40 may be selected individually or in any
combination as the anode for unipolar pacing with the ICD housing
411 serving as the cathode. For bipolar or multi-polar electrode
configurations, the electrodes within tip array 20, ring array 30
and ring electrode 40 may be selected in any combination. For
example, one or more of the electrodes within an array may be
selected to serve as an anode with any or all of the remaining
electrodes in the same array selected as the cathode.
Alternatively, electrodes may be selected from one array 20 or 30
to serve as the anode and from the other array to serve as the
cathode. Electrodes within arrays 20 or 30 may also be selected to
function with ring electrode 30 in a bipolar configuration.
[0059] The ICD 410 is preferably equipped with a capture detection
algorithm executed under the control of microprocessor 224.
Following delivery of a pacing pulse by ventricular pacer output
circuit 216, a desired pair of electrodes may be selected via
switch matrix 208 to sense for the evoked response. If an evoked
response is not detected, the pacing pulse amplitude may be
adjusted by pacer circuitry 212 under the control of microprocessor
224. Exemplary circuitry for detecting an evoked response is
described in previously incorporated U.S. Pat. No. 5,601,615 issued
to Markowitz et al., U.S. Pat. No. 5,324,310 issued to Greeninger
et al., and U.S. Pat. No. 5,861,012 issued to Stroebel.
[0060] Pacer timing and control circuitry 212 is coupled to lead
recognition circuit 250 for determining availability of pacing or
sensing paths. The lead recognition circuit 250 may include
impedance measuring circuitry such that valid lead pathways may be
identified when a measured impedance between electrodes falls
within an acceptable range. Lead recognition circuit 250 is coupled
to possible electrode configurations via switch matrix 208 along
signal line 252. A lead recognition apparatus and method that may
be used in ICD 410 is generally described in U.S. Pat. No.
5,534,018 issued to Wahistrand et al., incorporated herein by
reference in its entirety.
[0061] The microprocessor 224 includes associated ROM in which
stored programs controlling the operation of the microprocessor 224
reside. A portion of the memory 226 may be configured as a number
of recirculating buffers capable of holding a series of measured
intervals for analysis by the microprocessor 224 for predicting or
diagnosing an arrhythmia.
[0062] In response to the detection of tachycardia,
anti-tachycardia pacing therapy can be delivered by loading a
regimen from microcontroller 224 into the pacer timing and control
circuitry 212 according to the type of tachycardia detected. In the
event that higher voltage cardioversion or defibrillation pulses
are required, microprocessor 224 activates the cardioversion and
defibrillation control circuitry 230 to initiate charging of the
high voltage capacitors 246 and 248 via charging circuit 236 under
the control of high voltage charging control line 240. The voltage
on the high voltage capacitors is monitored via a voltage capacitor
(VCAP) line 244, which is passed through the multiplexer 220. When
the voltage reaches a predetermined value set by microprocessor
224, a logic signal is generated on the capacitor full (CAP FULL)
line 254, terminating charging. The defibrillation or cardioversion
pulse is delivered to the heart under the control of the pacer
timing and control circuitry 212 by an output circuit 234 via a
control bus 238. The output circuit 234 determines the electrodes
used for delivering the cardioversion or defibrillation pulse and
the pulse wave shape.
[0063] The flow chart shown in FIG. 10 is an overview of one method
for using the lead 10 in conjunction with the ICD 410. Although a
single chamber, left-ventricular device is depicted in FIGS. 8 and
9, a lead having one or more electrode arrays could be used with
atrial or ventricular single chamber devices, with dual chamber
devices or multichamber devices. These devices may be any of
implantable or temporary pacemakers, ICDs or cardiac monitoring
systems. Other than cardiac stimulation or monitoring systems, the
lead 10 and the method 500 of FIG. 10 to be described may also be
used in implantable or temporary neurostimulators or other medical
devices used for stimulating and/or sensing excitable tissue.
[0064] In regard to the implantable system illustrated in FIG. 8
and the ICD 410 shown in FIG. 9, the method 500 shown in FIG. 10 is
preferably performed under the control of microprocessor 224.
Method 500 allows the microprocessor 224 to automatically determine
which of the electrodes included in an electrode array provide the
optimal stimulation or sensing configuration by performing an
electrode scan. During the electrode scan, the pacing and/or
sensing thresholds of the available electrode combinations is
measured. Additionally, electrode lead impedance may be measured.
The optimal stimulation configuration is determined as the
electrode or combination of electrodes resulting in the lowest
pacing threshold that successfully captures the targeted tissue
without depolarizing non-targeted tissue. For example, in the
embodiment shown in FIG. 8, left ventricular capture is desired
without atrial capture or phrenic nerve stimulation. An optimal
sensing configuration may be identified as the electrode
configuration resulting in the highest signal amplitude or
signal-to-noise ratio. For the left ventricular application of FIG.
8, the optimal sensing configuration would provide the highest
R-wave amplitude or the greatest R-wave signal-to-noise ratio.
[0065] When the method 500 begins at step 505, the electrode
configuration selected is a default configuration. Typically, the
default configuration is the simultaneous selection of all the
electrodes included in an electrode array. This default
configuration will be used for designated pacing or sensing
functions until a more optimal configuration is identified. For
example, electrodes 25, 27 and 29 may be selected simultaneously to
serve as the anode during unipolar pacing as the default pacing
configuration. A default sensing configuration may be set as the
bipolar combination of the simultaneously selected tip array
electrodes 25, 27 and 29 paired with the simultaneously selected
ring array electrodes 35, 37 and 39.
[0066] At decision step 510, the microprocessor 224 determines if
an electrode scan is enabled. The electrode scan feature is
preferably enabled or disabled by a physician using an external
programmer in telemetric communication with the ICD 410. If the
electrode scan is disabled, the electrode selection remains in the
default configuration. Alternatively, a physician may manually
program an electrode configuration to override the default
selection.
[0067] If the electrode scan is enabled, a scan is initiated at
step 515. An electrode scan may be initiated by any of a number of
triggering events. Upon implantation of the lead 10 and ICD 410, a
detection of valid electrode pathways by lead recognition circuitry
250 may trigger the initiation of the electrode scan at step 515.
Other triggering events for an electrode scan may include detection
of a lead failure or a change in lead status. Reference is made to
previously incorporated U.S. Pat. No. 5,534,018 and to U.S. Pat.
No. 6,317,633 issued to Jorgenson et al., incorporated herein by
reference in its entirety. A scan may also be triggered manually,
on a scheduled or periodic basis, or in response to a loss of
capture.
[0068] At step 520, the microprocessor 224 performs a threshold
search on each electrode within an array individually and in any
number of desired combinations. A threshold search may be performed
according to methods known in the art. For example, a threshold
search may be performed by successively reducing the pacing pulse
amplitude until capture is lost. For an exemplary threshold search
algorithm, reference is made to U.S. Pat. No. 3,757,792 issued to
Mulier, incorporated herein by reference in its entirety.
[0069] In regard to the electrode configuration shown in FIG. 8,
electrodes 25, 27 and 29 in tip electrode array 20 and electrodes
35, 37, and 39 in ring electrode array 30 may be selected in any
unipolar, bipolar or multipolar configuration. For each
configuration selected, the left ventricular pacing threshold
and/or the R-wave sensing threshold is measured and stored in
memory at step 525. After measuring and storing the thresholds for
all desired electrode configurations, the configuration yielding
the optimal threshold is selected via switch matrix 208 at step 530
to operate as the designated configuration for the associated
pacing or sensing function. The pacing pulse energy and/or the
sensing threshold may also be set at step 530 according to the
stored threshold for the selected electrode configuration.
[0070] An electrode scan may be performed automatically as
described or semi-automatically under the supervision of a
clinician such that observation of any extraneous stimulation or
undersensing or oversensing may be made.
[0071] Final selection of the optimal electrode configuration may
then be made manually to eliminate electrode configurations
producing extraneous <stimulation or inaccurate sensing.
[0072] At decision step 535, the microprocessor 224 determines if a
preset amount of time, for example 24 hours, has elapsed. Once this
time is elapsed, an electrode scan may be automatically repeated.
Threshold changes may occur over time as electrodes become
encapsulated by fibrotic scar tissue or with changes in a patient's
physiologic condition, the use of drugs, or changes in disease
state. By repeating the electrode scan periodically, the optimal
electrode configuration and appropriate pacing energy or sensing
threshold settings may be updated in response to such changes.
[0073] The present invention is realized in an implantable medical
lead possessing one or more electrode arrays, each comprising
multiple electrodes that are electrically insulated from each
other. The electrodes within an array are preferably arranged
circumferentially in relation to the lead body and may be located
substantially in the area normally occupied by a conventional tip
or ring electrode.
[0074] A lead provided by the present invention includes a lead
body extending between a proximal lead end and distal lead end for
carrying multiple, insulated conductors. The conductors are each
electrically coupled to an associated electrode at or near the
distal lead end and to connectors at the proximal lead end for
establishing connection to an implantable medical device. The lead
may be equipped with a tip electrode array and/or one or more ring
electrode arrays comprising two or more, preferably three,
electrodes each. The electrodes within an array may be spaced from
each other around the circumference of the lead and/or along its
length. The electrodes within an array are electrically insulated
from each other by nonconductive material, such as a ceramic,
layered between each electrode in the array.
[0075] In one embodiment, a tip electrode array may be expandable
in order to improve the contact of one or more electrodes with a
targeted cardiac tissue site. Expanding the tip array
advantageously increases the spacing between electrodes to improve
sensing and stimulation performance. Moreover, expansion of the tip
array against the walls of a blood vessel stabilizes the lead
position. If used as an endovascular lead, blood will easily flow
between the expanded electrodes. A tip array may be expanded by
advancing an expansion member toward the distal lead end. The
expansion member is preferably conical such that as it is advanced
through an electrode head assembly carrying the tip array, the
widening circumference of the expansion member causes radial
expansion of the electrodes in the array.
[0076] In one embodiment the expansion member may be a fixation
helix mounted on a drive shaft that is coupled to a rotatable coil
extending to the proximal lead end. Rotation of the proximal end of
the coil causes rotation of the drive shaft, advancing the
cone-shaped helix. The helix may be used as an active fixation
device to further stabilize lead position. Alternatively, a
conically-shaped expansion member may be mounted on a drive shaft
having a screw-like head. A stylet equipped with a screwdriver-like
blade may be used to engage the shaft head and, when rotated, cause
advancement of the expansion member.
[0077] The lead provided by the present invention may be used with
a cardiac pacing device or ICD equipped with a microprocessor-based
control system for controlling device functions, a pulse generator
for generating electrical impulses to be applied to the heart, and
sense amplifiers for sensing cardiac signals. The device is
preferably equipped with a switch matrix for selectively connecting
one or more of the electrodes within an array in varying
combinations for associated sensing and pacing functions. For
example, one electrode within an array may be used for pacing and
the other two electrodes within an array may be used for sensing
the evoked response. Such a configuration advantageously overcomes
the problem of polarization artifacts normally encountered when
sensing for an evoked response using the same pair of electrodes as
used for pacing. The pacing device or ICD is also equipped with a
memory for storing cardiac data and, in particular, data relating
to the pacing threshold or sensing threshold associated with
various electrodes within an array.
[0078] In operation, the cardiac pacing device or ICD performs an
electrode scan to determine which electrode or combination of
electrodes within an array provides the lowest pacing threshold.
Once the electrode configuration providing the lowest pacing
threshold is identified, the control system of the device
automatically selects this configuration as the pacing electrode
configuration via the switch matrix. Alternatively or additionally,
if an electrode array is to be used for sensing, a sensing
threshold search may be performed in which the electrode(s)
providing the highest signal amplitude or greatest signal-to-noise
ratio may be determined and selected as the sensing electrode
configuration via the switch matrix.
[0079] According to the present invention, when the lead is placed
endovascularly for left heart applications, the electrode(s) within
an array that are in closest contact with the heart tissue may be
selected for stimulation and/or sensing. Stray current is
minimized. If phrenic nerve stimulation or undesired atrial pacing
occurs after implantation of a coronary sinus lead for left
ventricular pacing, an alternative electrode within a given
electrode array may be selected that still provides an acceptable
pacing threshold at the targeted ventricular tissue site without
extraneous stimulation.
[0080] According to the present invention, an electrode pair is
selected for sensing an evoked response that is in the same
vicinity of the paced tissue site but does not include the pacing
electrode. In addition, battery longevity of the stimulation device
may be improved by minimizing the surface area used to stimulate a
targeted tissue site. A smaller electrode surface area associated
with selecting one or two electrodes within an array increases the
pacing impedance resulting in less current drawn from the battery.
Furthermore, the electrode selection is "fine-tuned" by selecting
only the electrode(s) within an array that provide the lowest
pacing threshold, eliminating stray current and further extending
the useful life of the device. Device performance may be also be
improved by the ability to select an optimal sensing electrode
configuration such that accurate sensing of cardiac signals is
achieved.
[0081] The lead provided by the present invention may be stabilized
by an expandable tip array and still be readily deployed and
repositioned when used as an endovascular lead. Stabilizing the
lead position over time may ensure stable pacing and/or sensing
thresholds. By providing a lead with a reversible fixation device,
the lead is easily advanced or retracted through a vascular pathway
so that the surgical time required for positioning the lead may be
reduced, with fewer complications encountered. If an electrode
should fail, other electrodes within the same array may be used for
targeting the same tissue site.
[0082] Thus a medical lead that allows accurate targeting of
excitable tissue has been described and with which extraneous
stimulation may be avoided and improved evoked response sensing may
be achieved. The lead is readily deployed, secured and
repositioned, if necessary, and provides alternative electrode
configurations should a lead failure occur. A method for using the
medical lead has also been described in which optimal electrode
configurations may be automatically, or semi-automatically,
selected. While the medical lead and associated method included in
the present invention have been described according to specific
embodiments in the above disclosure, these embodiments should be
considered exemplary, rather than limiting, with regard to the
following claims.
* * * * *